Pack and a half condensing cycle pack with combined heat exchangers

BACKGROUND OF THE INVENTION

0001This invention relates to an air generation unit (AGU) suitable for an aircraft, and more particularly, the invention relates to a pack and a half air generation unit configuration utilizing two air cycle machines (ACM) with each preferably having two turbines.

0002AGUs typically include at least one ACM and at least one heat exchanger that receives air from a pressurized air source, such as bleed air from an engine, to provide cooled air to the aircraft cabin and cockpit. The AGUs may be packaged within the wings and/or tail section of the aircraft. Accordingly, it is desirable to provide an AGU having a very small package to limit the amount of aircraft structure that must be removed to accommodate the AGU. Furthermore, the AGU must provide sufficient cooling for the size of the aircraft.

0003A pack and a half AGU has been developed for use in a Dash 8-400 in which two ACMs share a common heat exchanger. The pack and a half configuration provides increased cooling and smaller packaging than two separate AGUs each having their own heat exchanger. The Dash 8-400 utilizes a three wheel air cycle machine having a fan, a compressor, and a single turbine.

0004The Dash 8-400 AGU includes a heat exchanger having primary and secondary heat exchangers. Bleed air is taken from an intermediate or high pressure stage of a turbine engine. The bleed air is pre-cooled within the primary heat exchanger with the heat being rejected to ram air and then communicated to the compressor of the ACM. After compression, the air is communicated through a secondary heat exchanger to a condenser. Condensed water vapor is extracted by a water collector, and the dehumidifier air is sent to turbine where the air is expanded to generate cold air. The cold air is sent to an environmental control system (ECS) that further conditions and distributes the air to the aircraft.

0005A Boeing 777 utilizes AGUs with a single ACM and single heat exchanger. The Boeing 777 ACM is a four wheel configuration that includes a fan, a compressor, and first and second turbines. The operation of the AGU is similar to the Dash 8-400 AGU, but the second turbine receives the cold air from the first turbine and further expands the cold air to produce subfreezing air. The second turbine produces air sufficient to cool larger aircrafts.

0006Very large commercial aircrafts are being developed capable of carrying up to 1,000 passengers or more. These large aircraft require AGUs capable of producing very cold temperatures. However, the design constraints for the aircraft require very small packaging with very high reliability. The Dash 8-400 AGU configuration produces conditioned air that is not sufficiently cold for such a large aircraft. The Boeing 777 AGU configuration provides sufficiently cold air, however, up to four or more AGUs would be required for such a large aircraft, which would necessitate removing significant aircraft structure and would significantly increase weight. Therefore, what is needed is an improved AGU having a small package, increased reliability, and sufficiently cold air for the needs of a large aircraft.

SUMMARY OF THE INVENTION AND ADVANTAGES

0007The present invention provides an air generation unit (AGU) including a pressurized air source, such as a turbine engine providing bleed air. First and second air cycle machines (ACM) are fluidly connected to the pressurized air source for receiving the air. A heat exchanger interconnects the first and second ACMs. The heat exchanger includes a primary heat exchanger that cools the air from the air source. The ACMs each include a compressor receiving the air from the primary heat exchanger to provide compressed air. The compressed air is sent to a secondary heat exchanger to be cooled. The compressed air is passed through a condenser and a water collector to remove moisture from the air for being sent to a first turbine. The first turbine expands the dehumidified air to produce a first conditioned air having a first temperature. The conditioned air may be as low as approximately 34° F. A second turbine further expands the conditioned air to produce a second conditioned air having a second temperature lower than the first temperature, which may be subfreezing.

0008The heat exchanger mechanically supports the first and second ACMs by flexible isolators, which accommodates the thermal expansion of the heat exchanger throughout the operation of the AGU. The condenser, water collector, and a manifold, which fluidly connect components of the ACMs, are centrally mounted in such a fashion to provide ease of access to the components when servicing the AGU. Accordingly, the above invention provides an improved AGU having a small package, increased reliability, and sufficiently cooled air for the needs of a large aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

0009Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

0010<figref idref="DRAWINGS">FIG. 1</figref> is a front perspective view of the present invention AGU;

0011<figref idref="DRAWINGS">FIG. 2</figref> is a side elevational view of the AGU shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0012<figref idref="DRAWINGS">FIG. 3</figref> is a bottom perspective view of the opposing side of the AGU shown in <figref idref="DRAWINGS">FIG. 2</figref>;

0013<figref idref="DRAWINGS">FIG. 4</figref> is an enlarged perspective view depicting the mounts between the heat exchanger and ACMs;

0014<figref idref="DRAWINGS">FIG. 5</figref> is a side exploded perspective view of a present invention AGU; and

0015<figref idref="DRAWINGS">FIG. 6</figref> is a schematic view of the present invention AGU.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0016An air generation unit (AGU) <b>10</b> is shown in <figref idref="DRAWINGS">FIGS. 1–3</figref>. The AGU <b>10</b> receives pressurized air from an intermediate or high pressure stage of an engine <b>12</b> through a bleed valve <b>14</b>. The pressurized air is conditioned by the AGU <b>10</b> to provide conditioned air to the aircraft.

0017The present invention AGU <b>10</b> includes first <b>16</b> and second <b>18</b> air cycle machines (ACM). The present invention ACMs <b>16</b> and <b>18</b> are a four wheel configuration including a fan <b>20</b>, a compressor <b>22</b>, and first <b>24</b> and second <b>26</b> turbines. The ACMs <b>16</b> and <b>18</b> are mechanically mounted to a shared or common heat exchanger <b>28</b>, which is mounted to the aircraft frame. A ram air inlet header <b>30</b> provides ram air to the heat exchanger <b>28</b> with the ram air exiting the heat exchanger <b>28</b> through ram air outlet header <b>32</b> and ram outlets <b>34</b>. The fan <b>20</b> helps to draw the air through the headers <b>30</b> and <b>32</b>.

0018As best shown in <figref idref="DRAWINGS">FIG. 1</figref>, the ram air enters the header <b>30</b> along a path I. The ram air passes through the heat exchanger <b>28</b> in a ram air flow path R, which is transverse to the path I defined by the inlet header <b>30</b>. Referring now to <figref idref="DRAWINGS">FIG. 2</figref>, the heat exchanger <b>28</b> includes a primary <b>36</b> and secondary <b>38</b> heat exchangers. The primary heat exchanger <b>36</b> is an air-to-air heat exchanger that cools the bleed air from the engine <b>12</b> prior to being compressed by the compressor <b>22</b>. The secondary heat exchanger <b>38</b> cools the compressed air from the compressor <b>22</b> prior to being sent to the turbines <b>24</b> and <b>26</b> for expansion and further cooling. The heat exchanger <b>28</b> is divided into first <b>40</b> and second <b>42</b> heat exchanger portions in the no flow direction to reduce the thermal stress on the heat exchanger <b>28</b>, which is the structural back bone of the AGU <b>10</b>. Specifically, the flow direction is indicated by the path I through the ram air inlet header <b>30</b>. Dividing the heat exchanger <b>28</b> along the direction of the path I reduces the thermal stresses on the heat exchanger <b>28</b> based upon mathematical models. However, splitting the heat exchanger <b>28</b> in the direction of the ram air flow R as it passes through the heat exchanger <b>28</b> has a less beneficial effect on the thermal stresses of the heat exchanger. The reduced thermal stress achieved by the split heat exchanger <b>28</b> extends the life of the heat exchanger <b>28</b> and AGU <b>10</b>.

0019The condenser <b>44</b> is arranged between the first <b>40</b> and second <b>42</b> heat exchanger portions so that the condenser <b>44</b> may be shared by the ACM <b>16</b> and <b>18</b>. The condenser <b>44</b> generates water vapor capable of being collected by the water collector <b>46</b> to dehumidify the air received from the secondary heat exchanger <b>38</b>. The water collector <b>46</b> is positioned beneath the condenser <b>44</b> to provide more efficient collection of water vapor by taking advantage of gravity. The condenser <b>44</b> and collector <b>46</b> are arranged centrally between the ACM <b>16</b> and <b>18</b>. A manifold <b>48</b> may be mounted between the condenser <b>44</b> and water collector <b>46</b> to provide an efficient centralized connection between the ACMs <b>16</b> and <b>18</b>, and other components of the AGU. As a result, many hoses and couplings may be integrated into the structure of the manifold <b>48</b>, and other centrally located components to increase reliability.

0020<figref idref="DRAWINGS">FIG. 4</figref> depicts the mounts between the ACM <b>16</b> and <b>18</b> and the heat exchanger <b>28</b> that further reduce the stress on the heat exchanger <b>28</b> and isolate the vibrations produced by the ACM <b>16</b> and <b>18</b> and prevent them from being transmitted to the aircraft through the heat exchanger <b>28</b>. The mounts <b>50</b> may be arranged in a triangular pattern between each of the ACM <b>16</b> and <b>18</b> and the heat exchanger <b>28</b>. Specifically, the mounts <b>50</b> may be arranged between each ACM and its respective heat exchanger portion <b>40</b> and <b>42</b>. The mounts <b>50</b> may include a bracket <b>52</b> connected to the heat exchanger <b>28</b> interconnected via a clevis <b>56</b> to a flexible isolator <b>54</b> mounted on the ACMs <b>16</b> and <b>18</b>. For other mounts <b>50</b>, the bracket <b>52</b> and clevis <b>56</b> may not be necessary. The heat exchanger <b>28</b> may be mounted to the air frame by frame mounts <b>57</b>, best shown in <figref idref="DRAWINGS">FIG. 5</figref>.

0021With continuing reference to <figref idref="DRAWINGS">FIG. 5</figref>, pressurized air from the engine enters through a bleed air inlet <b>59</b>. The high temperature bleed air passes through the primary heat exchanger <b>36</b> to cool the air to a temperature that is suitable for use with aluminum components. The cooled air from the primary heat exchangers <b>36</b> enters the compressor inlet <b>62</b> where it is compressed by the compressor <b>22</b> to provide compressed air. The temperature of the compressed air has been raised by the compressor <b>22</b> such that it must be passed through a secondary heat exchanger <b>38</b>. The compressed air exits the compressor <b>22</b> through the compressor outlet <b>64</b> and passes into the secondary heat exchanger <b>38</b>. The cooled air from the secondary heat exchanger <b>48</b> is communicated to the condenser <b>44</b> to form water vapor of sufficient character to be collected the water collector <b>46</b>. The dehumidified air exits the water collector outlet <b>68</b> and enters the first turbine inlet <b>69</b>. The dehumidified air is expanded by the first turbine <b>24</b> to produce a first conditioned air having a first temperature that may be as low as approximately 34° F.

0022The manifold <b>48</b> may include an upper <b>58</b> and lower <b>60</b> manifold portion secured to one another. The manifold <b>48</b> is centrally located between the ACMs and integrates numerous passageways that in the prior art have typically been defined by hoses secured between the ACM and other AGU components. The conditioned air from the first turbine outlet <b>70</b> is communicated through the lower manifold <b>60</b> and sent to the condenser <b>44</b> through condenser cold inlet <b>72</b>. The condenser <b>44</b> and water collector <b>46</b> remove additional moisture from the conditioned air from the first turbine <b>24</b>. The further dehumidified air is communicated through the manifold <b>48</b> through condenser cold outlet <b>74</b> into the second turbine inlet <b>76</b> where the air is further expanded by the second turbine <b>26</b>. The conditioned air temperature produced by the second turbine <b>26</b> is lower than the conditioned air temperature produced by the first turbine <b>24</b>. The conditioned air produced by the second turbine <b>26</b> may be of subfreezing temperatures, which better enables the AGU <b>10</b> to cool a large aircraft.

0023Air from a second turbine conditioned air outlet is sent to an environmental control unit (ECU) <b>84</b> for cooling of the aircraft. The second turbine conditioned air outlet <b>78</b> may have a first turbine air conditioned air outlet and other air sources communicated therewith to adjust the humidity and temperature of the air sent to the ACU <b>84</b>.

0024The ACMs <b>16</b> and <b>18</b> are four wheeled machines having a shaft <b>82</b> supporting the fan <b>20</b>, compressor <b>22</b>, and first <b>24</b> and second <b>26</b> turbines. The fan <b>20</b> is arranged within the ram air flow. The fan <b>20</b> pulls air through the heat exchangers <b>28</b> if the aircraft is not moving. To facilitate servicing and assembly of the AGU <b>10</b>, the ram air outlet header <b>32</b> may comprise ram air outlet header portion <b>86</b> secured to one another centrally by a seal <b>88</b>.

0025The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.